U.S. Pat. No. 6,168,143 describes such an air spring of the above-described type wherein the bead lies seal tight against the conical seat of the roll-off piston. The transition from the bead into the wall of the air spring flexible member is so configured that the air spring flexible member projects from the bead at an almost right angle to the piston axis and extends at the end of the bead facing toward the piston cover and lies against the piston cover. An annularly-shaped reinforcement core is worked into the bead and is, for example, a steel wire.
The flexible member wall of the air spring flexible member usually has one or several layers of a reinforcement fabric which takes up the loads occurring during operation. In order to be able to direct the forces into the roll-off piston, the reinforcement layers have to be wrapped around this reinforcement core. The reinforcement layers therefore form a loop the end of which must be guided back into the flexible member wall by a predetermined length to achieve the needed carrying capacity. This length cannot be made shorter as desired because of the maintenance of the necessary tensile strength of the reinforcement layer. In the region of the loop, the flexible member wall is especially stiff because of the doubled reinforcement layer.
The consequence of this arrangement is that the stiff region of the flexible member wall mostly extends beyond the roll-off edge (that is, the transition region from piston cover into the roll-off surface) and thereby makes more difficult the roll off of the air spring flexible member after a complete expansion of the entire air spring or, especially in the pressureless state, can even prevent the roll off. This causes the formation of folds in the air spring flexible member which can lead to a clamping and to a premature destruction of the flexible member wall.